Water ice photographed on Mercury

The Kandinsky crater on Mercury photographed by the Messenger space probe (Image ASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
The Kandinsky crater on Mercury photographed by the Messenger space probe (Image ASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

An article published in the journal “Geology” illustrates the discovery of water ice on the planet Mercury made ​​thanks to NASA’s Messenger (Mercury Surface, Space Environment, Geochemistry and Ranging) space probe. Several pictures show frozen water and other materials in permanently shadowed craters near Mercury’s north pole.

The theory that on Mercury there could be frozen water goes back many years. This possibility was taken into account despite the generally very high temperatures on the planet’s surface analyzing radar images taken from Earth. They revealed the existence of deposits at the poles that had the characteristics of ice water but it took years to verify that theory.

In 2012, thanks to the Messenger space probe it was possible to make more accurate analyzes from the planet’s orbit with various types of instruments. In 2012, Messenger allowed to gather evidence of the existence of ice at the north pole of the planet. Thanks to the extension of this probe’s mission, it was possible to take several photographs of some polar craters to have further confirmation of the existence of water ice.

Water on Mercury can be present only in perennial shadow so it wasn’t easy to get photographs that reveal the deposits. After several attempts, however, the mission team was able to obtain the desired images using the Messenger probe’s wide-angle chamber (WAC) of the Mercury Dual Imaging System (MDIS) instrument.

Photographs of deposits of water ice were obtained and sometimes also of other materials. Those are probably materials rich in organic compounds, which make this investigation even more interesting. Those deposits have been identified in craters such as Kandinsky and Prokofiev.

In the crater Berlioz, whose position is at a lower latitude, it’s too hot even in the permanent shadow to have water ice on the surface. Instead, under the surface it’s cold enough to have stable ice.

One of the main questions about these deposits regards their age. It’s a major problem because the answer has implications for the problem of the water arrival on all the rocky planets, including Earth. The images indicate that the polar deposits are composed of water arrived recently or that it’s regularly restored through some process.

Another interesting element of the research is the difference between Mercury and the Moon, which under other points of view are similar. In the Moon’s polar regions it’s colder than on Mercury’s but they look different. This problem also can help to better understand the processes of formation and evolution of Mercury, the Moon and the Earth as well.

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